Killer waves: How orcas hunt their favourite seal

Some killer whales are adept hunters, but picky eaters. New observations of "pack ice" killer whales roaming the waters off the Antarctic Peninsula show they dine almost exclusively on Weddell seals, which make up just 15 per cent of the seal population.

Robert Pitman and John Durban at the Southwest Fisheries Science Center in La Jolla, California, documented how these killer whales, or orcas, cooperatively stalk their prey.

Often, one killer whale pops up to identify a Weddell seal perched on an ice floe (shown), then alerts others in the area. A group - up to seven were observed - then charges the floe, spawning waves that wash the seal into the sea. Finally, the whales surround the seal, tiring it before they drown it by pulling on its hind flippers.

Genetic studies suggest these pack-hunting, seal-eating killer whales make up a unique species, distinct from other varieties that feast primarily on fish or minke whales.